Do I need special refractory tiles or "fire bricks" for an indoor fireplace or outdoor braai? How do I make sure the bricks don't crack and crumble from the heat?
Clay Bricks are fired at high temperatures to stabilise their structure, and have a high thermal mass which helps them insulate for heat. In a domestic fireplace or braai they are really a total "over specification". Refractory Bricks are normally rated from around 1600’C upwards. They are expensive and not easily available.
A braai will never reach this kind of heat and all facebricks are fired to around 1000 – 1250’C. The heat in the fireplace must get higher than this to have any effect on the brick. Generally your mortar joint will fail before the brick. What I always suggest to people is the following.
Build the outer skin of the sides of the braai/fireplace with a standard mortar mix (1 bag cement : 3 Barrows Sand) with brickforce and cavity ties. Build the inner skin with a well burnt clay face brick using a weaker mix (1 bag : 6 Barrows Sand) – this allows more joint movement and reduces cracking from heating.
Concrete bricks or any regular concrete product made with Portland cement cannot stand up to high temperatures and will disintegrate at the temperatures required by a pizza oven or braai.
With excessive heat, cement and mortar between the bricks can crumble. I recommend you use an air-set refractory cement (as oppose to a fire-set refractory cement), and minimize the joint space between the bricks – use “buttered joints” i.e. have the bricks very close together.
The heat to the walls of a grill is not that high (compared with the floor where the fire is built or the ceiling of a pizza oven) so ordinary tile cement can be used to adhere tiles.
- Laying Bricks